The generally known multi-function printer includes a tray drawer for carrying paper. The multi-function printer prints an image on the paper grasped from the tray drawer. When a user wants to know how much paper is left within the tray drawer, the user has to pull out the tray drawer. However, such practice requires an additional movement, and is inconvenient.
Therefore, how to enable the user to quickly and conveniently know how the quantity of the paper left within the tray drawer has become a prominent task for any person ordinarily skilled in the technology field of the invention.